Electrolytes for electrolytic level switches



gases, or solids, and mixtures thereof.

United States Patent F 3,293,383 ELECTROLYTES FOR ELECTROLYTIC LEVEL SWITCHES Kenneth C. Halliday, Jr., Port Washington, N.Y., assignor to The Bendix Corporation, a corporation of Delaware No Drawing. Original application Apr. 1, 1963, Ser.

No. 269,766. Divided and this application Oct. 8,

1965, Ser. No. 494,230

11 Claims. (Cl. 200-152) The present application is a division of copending U.S. application Serial No. 269,766, filed April 1, 1963, by Kenneth C. H-alliday, IL, and assigned to The Bendix Corporation, assignee of the present invention.

The invention relates generally to electrolytic level switches and in particular to electrolytes used in such switches.

Electrolytic level switches are device-s which have variable electrical characteristics in response to their orientation in a force field, which usually is a gravity force field. The mechanical details of their constructions are not of concern in this invention, which is limited to the chemical constituents of the switch, as they may be liquids, The electrolytes of this invention are appropriate to a variety of level switch constructions; which include but are not limited to those describedin F. Cid US. Patent No. 2,890,430, assigned to the same assignee as the present application.

In a generalized switch construction, there is an envelope including at least two electrodes, all hermetically sealed to contain the liquid electrolyte (i.e. liquid phase component) and a gas bubble (i.e. gas phase components). The liquid member is an electrolyte, i.e. conducts electricity, while the gas member must be effectively an insulator.

It is further desirable that the liquid and gas remain substantially in the same volumetric equilibrium with each other over the widest practical temperature range; and particularly that no appreciable solid phase (freezing, etc.) appears at lower temperatures, and gas phase (boiling) appears at higher temperatures since this would interfere with switch response. As is well known, aqueous electrolytes are intolerant of low temperatures (i.e. salt water freezes) and suitable organic solvents for electrolytes are severely limited, cf. Moeller, T., Inorganic Chemistry, New York, Wiley (1952), pp. 355-357.

At the serviceable upper temperature extreme of the switch, the electrolyte must not boil. As an example, consider an electrolyte of aqueous methanol and A1 to /2 molar alkali halide. It is found that as operational temperatures rise, methanol withdraws from liquid into a gas phase resulting in super-saturation of salt in the residual liquid phase; when tilt action takes place, there occurs deposition of a semi-conductive salt on the switch walls over the wash angle. Consequently, the switch action becomes erratic and inaccurate, with the open and closed electric resistances being less sharply defined. Thus to provide an electrolytic switch suitably functionable into the region 100-125 C., some higher boiling point solvent systems are desirable.

It has been found that introducing an extra halogen component into various organic liquids that have wide bands of liquid phase across the temperature range of interest sufficiently improves the solubility of the salts enabling the total combinations to function as a satisfactory electrolyte. As an example, the halogen component may be solid phase iodine or liquid phase bromine, in amounts appropriate to maintain a liquid phase temperature tolerance in admixture with low temperature tolerant solvents. The halogen may be in organic phase, as pseudo-compounds, characterized by a dark brown or reddish solution (e.g. iodine in propyl-propionate). The pseudoice compounds contribute suitable physico-chemical characteristics to the electrolyte and comprise the types, classes and combinations defined herein.

Suitable organic solutions may be prepared from alcohols, esters, and ester alcohol mixtures. It is more appropriate to use compounds of three through twelve carbons because shorter hydrocarbon chain groups develop low boiling compounds that limit the upper temperature tolerance of the system, while longer hydrocarbon chains are of limited use due to appearance of solid phases at low temperature.

We consider first the aliphatic normal alcohols having a liquid phase in the temperature range 50 C. to C. Since both methanol and ethanol have boiling points well below 100 C. and are subject to the evap-' oration limitations previously defined, we begin with n-propanol (which has a liquid phase at temperatures 100 C. to +98 C.) and continue with the homologous series n-butanol (-89 C. to +117 C.), n-pentanol (78 C. to +138 C.) and n-hexanol (51 C. to +157 0.). The lower temperature (freezing point) now becomes limiting since n-heptane freezes at -34 C.

Adding a few percent of a halogen establishes a two component system, we obtain a useful characteristic in that like atoms tolerate each other, and we can now add an alkali metal salt of the halogen to produce the electrolyte. As is well known the two-component alcohol halogen system is classified as a nonelectrolyte (Hildebrand, Solubilities of Nonelectrolytes, New York, Reinhold Publishing Corporation, 1936), but using the twocompound alcohol as a carrier bi-solvent, it is transformed into a useful electrolyte for certain types of electrolytic switches; Some appropriate examples of these combinations are illustrated.

The following examples are illustrative of electrolytes falling within the scope of the invention disclosed and claimed in the parent US. application Serial No. 269,776. It will be understood that such examples are in no Way limitations of the invention since numerous other electrolyte compositions can readily be prepared in light of the guiding principles disclosed herein.

Example 1 n-Propanol cc 100 Iodine grams 12.7 Sodium iodide do 5.1

Example 2 n-Butanol cc 100 Iodine grams 15 Sodium iodide do 7.5

Example 3 n-Pentanol cc 100 Iodine gra'ms 19.1 Sodium iodide do 5.1

Example 4 n-Hexanol cc 100 Iodine grams 19.1 Sodium iodide do 4.5

Example 5 n-Propanol cc 100 Bromine grams 12.7 Sodium bromide do 5.1

The elfectivity of the alcoholic systems is nevertheless still limited by the liquid phase spread; if this can be widened, a more desirable electrolyte can be produced. We now consider the chemicals known as aliphatic linear esters, particularly those containing at least six carbon atoms and not more than 12 carbon atoms and again limiting ourselves to those that are not solid above -40 C. Examples of suitable aliphatic linear esters falling within the scope of the invention and claimed herein include;

n-Propyl-propionate (liquid in a temperature range of 75 C. to +123 C.) n-Butyl-propionate (89 C. to +145 C.) n-Pentyl-propionate (73 C. to |l64 C.) n-Hexyl-propionate (57 C. to +190 C.) n-Heptyl-propionate (l C. to +208 C.) n-Propyl-butyrate (95 C. to +143 C.) n-Butyl-butyrate (-91" C. to +164 C.) n-Pentyl-butyrate- (-73 C. to +185 C.) n-Hexyl-butyrate (-7E C. to +205 C.) n-Heptyl-butyrate (-58" C. to +275 C.) n-Octyl-butyrate (55 C. to +244 C.) n-Propyl-valerate (80 C. to +167 C.) n-Butyl-valerate (92 C. to +186 C.) n-Amyl-valerate (-79 C. to +204 C.) -n-Hexyl-valerate (-63 C. to +224 C.) n-Propyl-caproate (69 C. to +185 C.) n-Butyl-caproate (-92 C. to +186 C.) n-Amyl-caproate (47 C. to +222 C.) n-Hexyl-caproate (--55 C. to +245 C.)

Again we can establish electrolyte systems by adding free halogen to the ester then develop the electrolyte with the addition of A to /2 molar halide salt. Illustrations fol-low, wherein the halogen is present in amounts of approximately 3 to 4 times that of the alkali metal salt.

Example 6 n-Butyl butyrate liter 1 Iodine grams 150 Potassium iodide do 45 Example 7 n-Propyl-propionate cc 100 Iodine grams 15 Sodium iodide do 4.5

Example 8 n-Butyl-propionate cc 100 Iodine grams 12 Potassium iodide do 4 Example 9 n-Hexyhcaproate cc 100 Iodine "grams-.. 20 Sodium iodide d o 5.1

Example 10 n-Propyl-propionate cc 100 Bromine grams Sodium bromide do 4.5

The pure ester systems are not adequately time stable because of internal chemical reactions. As is well known, esterification is a reversible reaction, and under conditions that can occur in an electrolytic switch, the ester may split into its acid and alcoholic members. This would be followed by saponification of the acid into an undesirable soap phase. It is accordingly advisable to take advantage of the mass law relationship to include additional alcohol so that the acid component does not get free. It is better to use symmetrical esters, which then require one alcohol without the possibility of rearranging the ester to a smaller arrangement, although nonsymmetrical esters will work satisfactorily. A suflicient amount of alcohol should be added to preserve the stability of the ester without applying an excess of alcohol that will produce an alcohol type electrolyte. It has been found the ratio of approximately /3 ester to /3 alcohol is most satisfactory. Typical examples of these ester-alcohol electrolytes falling within the scope of the invention disclosed and claimed in copending divisional application U.S. Serial No. 494,262, filed October 8, 1965,

by Kenneth C. Halliday, Jr., and assigned to The Bendix Corporation, assignee of the present invention, are now defined in the following examples.

Example 11 Propyl-propionate cc 65 Propanol cc 35 Iodine grams 20 Sodium iodide do 4.5 7 Example 12 Amyl-valerate cc n-Amyl-alcohol cc 20 Iodine grams :10 Sodium iodide do 5 Example 13 Butyl-butyrate cc 66 n-Butanol cc 34 Iodine grams 12.7 Sodium iodide do 5.1

Example 14 Propyl-propionate cc 65 Propanol cc 35 Bromine grams 20 Sodium bromide do 4.5

Example 15 Amyl-propionate cc 7O n-Pentanol cc -30 Iodine grams 19.1 Sodium iodide do 5 These electrolytes constitute an improvement over the existing electrolytic switch chemicals because practical considerations dictating the selection of useful switch envelopes, electrode materials, etc. result in envelopes and electrodes of material which cause chemical changes in the electrolyte so that aside from phase stability in the temperature environment, the fiuids physico-electrical characteristics decay in time. As is well known, the alkaline-halide electrolytes heretofore used do react chemically with metal electrodes, with glass and metal envelopes, etc. of the switch. Accordingly, my improvement in electrolytes includes better compatibility with both the carbon electrodes, etc. of the above cited Cid patent as well as functionability with the noble metal electrodes used in other switches.

While the invention has been described in detail, it will be understood that various modifications may be made without departing from the essential teachings set forth herein and which are delineated in the appended claims.

What is claimed is:

1. An electrolyte for use in a level switch, consisting essentially of a liquid solution in an aliphatic linear ester having at least 6 carbon atoms and not more than 12 carbon atoms and having a liquid phase above -40 degrees ce-ntigrade, of a halogen selected from the group consisting of iodine and bromine and an alkali metal salt selected from the group consisting of iodide and bromide of potassium and sodium, the alkali metal salt being present in amounts of approximately 4 to 5 grams per cubic centimeters of ester and the halogen being present in amounts of approximately 3 to 4 times that of the alkali metal salt.

2. An electrolyte in accordance with claim 1 wherein the halogen is iodine and the alkali met-a1 salt is sodium iodide.

3. An electrolyte in accordance with claim 1 wherein the halogen is bromine and the alkali metal salt is sodium bromide.

4. An electrolyte in accordance with claim 1 wherein the ester is n-propyl-propionate.

5. An electrolyte in accordance with claim 1 wherein the ester is n-butyl-propionate.

6. An electrolyte in accordance with claim 1 wherein the ester is -n-pentyl-propionate.

7. An electrolyte in accordance with claim 1 wherein the ester is n-hexyl-propionate.

8. An electrolyte in accordance with claim 1 wherein the ester is n-:heptyl-propionate.

9. In a liquid level switch which includes a closed recept-acle containing an electrolyte and electrodes having a surface adapted to contact said electrolyte to provide a current conducting path between said electrolyte and said electrodes, the improvement wherein said electrolyte consists essentially of a liquid solution in an aliphatic linear ester having at least 6 carbon atoms and not more than 12 carbon atoms and having a liquid phase above 40 degrees centigrade, of iodine and an :alkali metal iodide selected from the group consisting of sodium iodide and potassium iodide, the iodine being present in amounts of approximately 3 to 4 times that of the amounts of the alkali metal iodide, and the alkali metal iodide being present in amounts of approximately 4 to 5 grams per 100 cubic centimeters of the ester.

10. In a liquid level switch which includes a closed receptacle containing an electrolyte and electrodes having a surface adapted to contact said electrolyte to provide a current conducting path between said electrolyte and said electrodes, the improvement wherein said electrolyte consists essentially of a liquid solution in an aliphatic linear ester having at least 6 carbon atoms and not more than 12 carbon atoms and having a liquid phase above degrees centigr-ade, of bromine and sodium bromide, the amount of the bromine being approximately 3 to 4 times that of the amount of the sodium bromide, and the sodium bromide being present in the amounts of 4 to 5 grams per cubic centimeters of the ester.

11. In a liquid level switch which includes a closed receptacle containing a liquid electrolyte and electrodes having a surface adapted to contact said electrolytes to provide a current conducting path between said electroly-tes and electrodes, the improvement wherein the electrolyte comprises a solvent of n-propyl-propionate and a solute of sodium iodide, and iodine, the solute being present in proportions of approximately 15 grams iodine and 4.5 grams of sodium iodide per 100 cubic centimeters of n-propyl-propion-ate.

References Cited by the Examiner UNITED STATES PATENTS 2,250,212 7/1941 Smits 25262.2 2,387,313 10/1945 Wilson 33844 X 2,713,726 7/1955 Dixson 33844 X 2,764,653 9/1956 Schoeppel 200--152.l0 2,852,646 9/1958 Bro-adley 338-44 2,927,987 3/1960 Uhl 200152.10

HELEN M. MCCARTHY, Primary Examiner.

TOBIAS E. LEVOW, Examiner.

R. D. E-DMONDS, Assistant Examiner. 

1. AN ELECTROLYTE FOR USE IN A LEVEL SWITCH, CONSISTING ESSENTIALLY OF A LIQUID SOLUTION IN AN ALIPHATIC LINEAR ESTER HAVING AT LEAST 6 CARBON ATOMS AND NOT MORE THAN 12 CARBON ATOMS AND HAVING A LIQUID PHASE ABOVE --40 DEGREES CENTIGRADE, OF A HALOGEN SELECTED FROM THE GROUP CONSISTING OF IODINE AND BROMINE AND AN ALKALI METAL SALT SELECTED FROM THE GROUP CONSISTING OF IODIDE AND BROMIDE OF POTASSIUM AND SODIUM, THE ALKALI METAL SALT BEING PRESENT IN AMOUNTS OF APPROXIMATELY 4 TO 5 GRAMS PER 100 CUBIC CENTIMETERS OF ESTER AND THE HALOGEN BEING PERCENT IN AMOUNTS OF APPROXIMATELY 3 TO 4 TIMES THAT OF THE ALKALI METAL SALTS. 